Coating by evaporating metal under vacuum



April 21, 1953 E. E. CHAD'SEY, JR 2,635,579

COATING BY EVAPORATING METAL UNDER VACUUM Filed Dc. 1, 1949 INVENTOR.

BY EARL E. CHADSEY, JR.

@Zdw W ATTORNEY Patented Apr. 21, 1953 COATING BY EVAPORATING METAL UNDER VACUUM Earl E. Chadsey, Jr., Newton, Mass., assignor to National Research Corporation, Middlesex County, Mass, a corporation of Massachusetts Application December 1, 1949, Serial No. 130,453

4 Claims.

This invention relates to coating and more particularly to improved apparatus and methods for feeding a metal to a metal-evaporating crucible in a vacuum coating system.

A principal object of the present invention is to provide an improved metal-feeding apparatus for replenishing metal to be melted and vaporized in a crucible positioned within a vacuum coating chamber.

Another object of the invention is to provide an improved apparatus, of the type described above, which is capable of feeding metal accurately over long periods of time without interfering with eflicient and uniform coating operations, the metal-feeding apparatus being arranged so that there is a minimum amount of condensation of metal vapors thereon.

Still another object of the invention is to provide improved methods for feeding pellets, of the metal to be coated, to a metal-evaporating means.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangement of parts, and the process involving the several steps and the relation and the order of one or more of such steps with respect to each of the others which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

Fig. 1 is an exaggerated, diagrammatic, partially sectional View of one preferred embodiment of the invention; and

Fig. 2 is a fragmentary view similar to Fig. 1 showing a modification of a portion of the apparatus of Fig. 1.

In general the present invention is directed to improved apparatus and methods for feeding metal from a supply thereof to a metal-evaporating means in a vacuum coating device. Since the time necessary to evacuate the coating chamber to the requisite low pressure is quite considerable, it is extremely advantageous to provide continuous operation of the metal-evaporating means. This can only be accomplished by providing a means for replenishing the metal as it is evaporated. For maximum efficiency and uniformity of coating, the metal-feeding means should not be so positioned as to interfere with h on the substrate.

the vapor stream passing between the metalevaporating means and the substrate to be coated. In the present invention the above advantages are achieved by the novel arrangement of the various elements comprising the metal-feeding apparatus. In one preferred formof the invention, the apparatus includes a vacuum-tight chamber and a means for evaporating the metal to be coated on the substrate. This metal-evaporating means preferably comprises an openmouthed crucible. The substrate to be'coatedis arranged to be fed above the crucibleso that the metal vapors rising therefrom will condense The apparatus includes. a means for holding a'supply of pellets of the coat-' ing metal, and means for feeding individual pellets from the supply. Associated with the feeding means is a means for guiding a fed pellet along a path spaced from the crucible and extending below the mouth of the crucible. Positioned at the bottom of the path of the pellet-is a deflecting means which is arranged to deflect the pellet and to impart an upward and lateral motion to the pellet so as to cause the pellet to travel, under the influence of kinetic energy acquired during its downward movement, in an arc terminating in the open mouth of the crucible.

Referring now to Fig. 1 there is shown one preferred form of the invention wherein the deflecting means comprises a bounce plate upon which the pellet falls and then rebounds into the crucible. In the apparatus of Fig. 1 there is provided a vacuum-tight chamber l0 arranged to be evacuated by a suitable vacuum pumping system IS. The material to be coated, such as a flexible, nonmetallic substrate, is indicated at [2 as being arranged to be fed from a supply (not shown) to a windup coil l3 therefor. The metal-evaporating means, generally indicated at I4, is shown in a preferred form as comprising a metal-evaporating crucible I6 including a lip i8 defining the mouth of the crucible. This crucible holds a predetermined quantity of the coating metal 20, this metal 20 being heated to evaporation temperature by a suitable source of heat, such as a radiant heating element 22. Crucible I6 is preferably supported within an outer refractory crucible 24 which also serves the additional function of preventingheat loss from the radiant heating element 22. The particular type of crucible and heating element shown in Fig. 1 is described and claimed in the copending application of Noble E. Hamilton, Serial No. 117,444, filed September 23, 1949, now abandoned. The metal replenishing system, with which the mi present invention is particularly concerned, is shown diagrammatically as comprising a number of pellets 26 contained in a suitable supply 28 therefor. For removing the individual pellets from the supply 28, there is provided a feeding means-gsuchas a-wheel 30, having aplurality of pellet-engaging notches 32 in the periphery thereof. This wheel may be suitably rotated .by a number of mechanisms employed for introducing mechanical motion into a vacuum. system. Examples of such mechanisms are shown in Industrial and Engineering Chemistry, Vol.39, page 1065 (1947), and U. S. Patents 2;482,329, 2,4l;'720

(Dimmick) and 2,403,199 '(Swope) Aslthe wheel 30 rotates in a counterclockwise direction, each notch 32 picks up an individual pellet 26 and deposits this pellet 26 in a trough -34; *Pos'itioned below and spaced from the end of trough 34- is a In the operation of the above-described device, a supply of pellets 25 may be initially provided in the metal-evaporating crucible [5. After the vacuum chamber l0 has been evacuated, the heater element 22 is energized to raise the tem- -perature-of. the crucible lBtto. the .point Where "the levelof .themetal in the crucible drops and an additional pellet is fed thereto.

'passesithe supplylfl, it picks up an individual pelletand drops this pellet into the trough 34.

"The pellet then rolls .doWn the trough, rolls off the end of the trough, strikes the bounce plate *35', and rebou'ndsinto the open 'moutliiof the -crucible." The rotation of the wheel '30-- maybe accomplished manually by observingthedevelof molten metal-in the crucible, or it may =be operated automatically in accordance with a predetermined cycle.

*The present invention has a number ofadvantages. It is accurate and mechanically-simple. It provides a coating apparatus' which' 'is 'capable of long runs so asto give a maximum output of 'coatedmaterial'from a particular coating apparatus." There isnocondensationofthe coating metal on the'movingparts otthe-spelletfeeding mechanism. Additionally, I the present invention has the extremely important advantageof providing no interference Withtheivapor stream emanating from the metal-evaporating 'cruciblei This is of'the utmostimportance where uniform coatings of wide areas-of a substrate-are to be provided. It completely eliminates any -shadows-- which' inight' arise in'the evaporated coating on the substrate.

"In FigA 2-there is shown 'another'modification 'of the invention wherein the defiec'tingimeans comprises a portion of t'he apparatus' whiclrrelatively gradually changes the 'direct-ionbfirthe motion of i the pellet rather thanircausingfrthe abrupt changeofdirection 'embodie:li"in-- the bounce plate '35 of" Fig. 1. In Fig; 2 where like numbers refer tollike elementsin-..the.preceding figure, the pellet-deflecting means; comprises a tube '40 which constitutes .an.iextension "of the trough'i34. This tube .49 is preferably covered on-that portion thereof which extends through 'the shieldi38.l Fig. 2additionallyishows a:.modification of the crucible which can be appliedto the Fig. 1":10111'1';Of'fthIGliXIYEII GiOII, and whichtcomprises :the addition. of asbarrier T 52 acentpone lip of the crucible. This barrierAZ has the;,func'- tion:ofdefiectingtbackintozthe crucible any; pellet which, duetoatgreater weightor. a lower-icoefficient of friction or other irregularity,.:f0llows, during its :course'of flight; afpathrindicated at 2.6a rather "thanthe normal. path 26b. for which thezapparatus is preferably adjusted.

In thoseicases where'there is atendencycfethe coating metal'to'condenseon the barrier element 42; this element mayxbe'heatedto a temperature "sufiicient to prevent such;icondensation;:-'or;to a temperatureitsuchl .thattany condensed; metal will .drip back-iontoi lip I84. It =can thus be seen that barrier 42 in 'EfiECtfSEIVES as: an'extension of ;;lip ill of the crucible. rln the'operation'of the Fig. 2 device, the individual 'p'ellets, rollingdown the trough: 34.an d

bounce plate 36. This-bounce plate 36 is preferably positioned belowthe level of the lip liiof T the -open-.mouth'ed cru'cible I 6 so as: to be removed J from-'the'"vapor streamemanating'from "fthemolten metal 20 in the "crucible. For preventing travel ofany-portion"of thevapor'stream P to the metal-feeding mechanism;- there" is' pro- "vided ashield-38. As'can be' seenf-the'end of the'sh'ield"38; adjacent the'topof the bounce plate 35;'"extendsbelow the direct-line path of vapor 'emanatingfrom' the surface of the molten pool 20. Themajority of the vaporemari-ating from-"the surface of themolten'metal travels nearly normally from this surface, and the greatest-concentration of'these "vapors is there- .i. forewithin a cone having outerrlimits about-45 witlrrespect to the normal. Thus, a verysmall percentage of=the metalvapor' diffuses downbe- T low the lip-"of-the'crucible"andbelow thebottom "end 'of-sh'ield3 8.

The bouncepl'ate 35: is sufllciently low and-so j "positioned thatithekinetic *energya'cquiredby an ."ihdividua'l pelletZfif during'itsrolling down-the :ftrough' fl"andfallingfrom the-end of th'e trough tothe bounce plate; is s'ufiicient to cause the pe1 let 2 6 to "rebound 'along"the" curved "dotted-line path into" the mouth of the crucible I5. The angleat which the'pellet strikes the bounce plate, the kinetic energy ofthe'pellet, and the' rebound characteristics of? :the bounce "plate "are so ad- "justedthat"the curved-path 'of the pellet terminatesimthecruoible mouth.

In apreferred'form of "the invention,"where ifthe Ineta'l to'be evaporated isaluminum the metal evaporatingcrucible *l 6- preferably comprises awarbon graphite crucible lined with zirconium carbide of the type described in "the" copehding "aapplication "of 'Ch'a'dsey etalt} -Ser'ial- NOL' 1 171124, 'filed Septembe1"-22 1949. The otlier elements, such-as" the" heater element 22' and the outer 'crucible'24, are also" preferably formed of materialsspecifled inthepreviously mentioned-Ham- -*ilton application. The bounce plate Git-preferably comprises a relatively soft, resilient mate rial which will give a-relatively high-percentage of'bouncetd-the' aluminum -"pellet 2 The pre- *-ferred'=material for this purpose "comprises the "carbomgra'phite combinatiorr sold under the "*tradenamebf "Graphitar',- this material being soft enough so as not to flatten the aluminum 'peIlet When thep'ellet strikes-the "-Graphitar "and'having a suflicientresiliencyto"give a re- 'ibouhd offapproximately 7O of the height" from "which the pellet'has'fallen. This allows the "'bounceplatetobespaced both a substantial distance'froni'themouth ofthe crucible and a substantial distance below the mouth'of the crucible.

through the curved pipe 40, contain a sufficient kinetic energy so as to follow a trajectory which terminates within the crucible mouth. As can be seen from Fig. 2, the open end of the curved tube 40 is positioned below and spaced from the mouth of the crucible so as to be removed from the vapor stream emanating from the crucible. It thus has the advantages enumerated in the preceding discussion of Fig. 1.

The metal-evaporating crucible, shown in the drawings, can be considerably modified. For example, it may be of the type described in the previously mentioned copending application of Chadsey et al., or it may comprise other types of metal-evaporating crucibles shown in the prior art. Numerous examples of such crucibles are shown in the following U. S. Patents: 1,584,728, Case, May 18, 1926; 2,074,281, Sommer, March 16, 1937; 2,157,478, Burkhardt et al., May 9, 1939; 2,337,679, Osterberg, December 28, 1943; 2,374,331, Cooke, April 24, 1945; 2,378,476, Guellich, June 19, 1945; 2,382,432, McManus et al., August 14, 1945; 2,384,500, Stoll, September 11, 1945; 2,387,- 970, Alexander, October 30, 1945; 2,405,662, Mc- Manus et al., August 13, 1946; 2,423,729, Ruhle, July 8, 1947; 2,554,902, Godley, May 29, 1951; 2,562,182, Godley, July 31, 1951.

Additionally, it should be apparent that other feeding means than those specifically illustrated may be embodied in the invention without departing from the scope thereof. Additionally, a suitable modification of the structure for imparting kinetic energy to the individual pellets may be incorporated in a structure of the type shown. For example, the kinetic energy imparted to the pellet may be provided by a spring mechanism or other source of energy rather than, or in addition to, the force of gravity utilized in the illustrated embodiments.

In some cases it is desirable to vary the rate of feed of the pellets. In such cases the variations of the speed of rotation of wheel 30 may be quite substantial and the kinetic energy of the pellet 26 fed to the top of the trough 34 is apt to vary considerably, with a consequent variation of the speed with which the pellet leaves the lower end of trough 34. This disadvantage may be readily overcome by modifying the apparatus of Fig. 1 so that the plane of rotation of wheel 30 is normal to the plane of the trough. With this modification each pellet starts to roll down the trough with virtually no initial velocity.

Since certain changes may be made in the above apparatus and process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description, or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The process of replenishing a supply of metal in an open-mouthed, metal-evaporating crucible positioned in a vacuum-tight coating chamber which comprises providing a supply of pellets of said metal, imparting a predetermined amount of kinetic energy to an individual pellet so as to cause said pellet to travel in an are commencing at a point laterally spaced from and below said crucible mouth and terminating in the vicinity of the crucible mouth, and shielding the point of commencement of said are from the metal vapor stream emanating from said crucible mouth.

2. Apparatus for coating a substrate with a metal by evaporating said metal in a vacuum and condensing said metal on the substrate, said apparatus comprising a vacuum-tight chamber, an open-mouthed crucible for melting and evaporating said metal, means for positioning said substrate above said open mouth of said crucible, means for holding a supply of pellets of said metal, means for feeding individual pellets from said supply and along a path spaced from said crucible and extending downwardly below the mouth of said crucible, and means for deflecting said pellet at the bottom of its path to impart an upward and lateral motion to said pellet to cause said pellet to travel, under influence of kinetic energy acquired during its downward movement, in an arc terminating in said open mouth of said crucible, said deflecting means being shielded from the metal vapor stream emanating from said crucible mouth.

3. The apparatus of claim 2 wherein said open mouth of said crucible includes an outwardly and upwardly extending lip means.

4. The apparatus of claim 3 wherein a portion of said lip means is enlarged to assure termination of said path within said mouth.

EARL E. CHADSEY, JR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,570,949 Cunningham et al. Jan. 26, 1926 1,707,294 Woodson Apr. 2, 1929 2,074,281 Sommer Mar. 16, 1937 2,151,737 Bryan Mar. 28, 1939 2,153,786 Alexander et al. Apr. 11, 1939 2,387,970 Alexander Oct. 30, 1945 2,426,377 Smith Aug. 26, 1947 2,440,135 Alexander Apr. 20, 1948 

